The present invention relates to systems and methods for determining engine oil temperature at engine startup.
Engine oil temperature is one of many engine operating parameters which may be used to control an internal combustion engine. For example, engines having variable cam timing (VCT) which uses oil pressure to alter the timing of the intake and/or exhaust valves may use engine oil temperature to determine when VCT operation is allowable or desirable.
Prior art strategies for determining engine oil temperature used an oil temperature sensor to directly measure the temperature, or inferred oil temperature from various other engine sensors and operating conditions. Calculating oil temperature provides various benefits associated with elimination of a physical sensor on the engine. However, accurate inferred oil temperature during running of the engine, as described in U.S. Pat. No. 5,633,796 for example, relies on an accurate oil temperature at engine startup. Known strategies for inferring engine oil temperature at startup accounted for only the most common startup conditions and were therefore occasionally inaccurate. For example, the inventors herein have recognized that these strategies did not account for engine block heaters, engine restarts after a short drive followed by a short shut-down (or soak), or oil temperature changes if the engine was not cranked for some time period after turning the key to the xe2x80x9cONxe2x80x9d position. The latter situation may occur when operating vehicle accessories for a period of time prior to starting the vehicle, such as when listening to the radio, for example.
An object of the present invention is to provide a system and method for more accurately determining engine oil temperature at engine startup without using an oil temperature sensor.
In carrying out the above object and other objects, advantages, and features of the present invention, a system and method for determining engine oil temperature at engine startup for an internal combustion engine include retrieving a shutdown engine oil temperature value previously stored in memory prior to the engine being shutdown, determining a value indicative of engine coolant temperature, determining elapsed time between engine shut down and startup, and calculating the engine oil temperature at startup based on the engine coolant temperature value, the shutdown engine oil temperature value retrieved from memory, and the elapsed time.
The present invention provides a number of advantages. For example, by more accurately determining engine oil temperature at startup, the present invention is capable of improving driveability, particularly for VCT engines. The present invention eliminates the need for an engine oil temperature sensor for applications which require an accurate temperature.
The above advantages and other advantages, objects, and features of the present invention, will be readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
FIG. 1 is a block diagram illustrating operation of one embodiment of a system or method for determining engine oil temperature at startup according to the present invention;
FIG. 2 is a flowchart illustrating operation of one embodiment of a system or method for determining engine oil temperature at engine startup according to the present invention; and
FIG. 3 is a more detailed flowchart illustrating operation of a system or method for determining engine oil temperature at engine startup according to the present invention.